As others have said before, Natt's place is very much to be recommended.
She is a first rate host: extremely nice, very accommodating, replies nearly instantaneous. There is absolutely nothing negative to say about her.
The place itself is clean and has about everything you could wish for. The condo is convenentiely located 100 meters away from the skytrain. The apartment is on the top floor and, while not exactly big, certainly spacious enough for one or for two people to spend the evening. During the day there is some street and construction noise to be heard (as nearly everywhere in Bangkok, certainly along the main roads), but nothing major, but at night it is quiet and I never had trouble sleeping throught my stay (and I'm a light sleeper).
The facilities are overall nice. The gym is your standard condo gym, not much use if you powerlift, but suitable for your average workout. The pool is mostly in the shade, the water rather on the cool side and the depth pretty shallow (which is again standard). But it IS suitable for actual swimming and you will probably have it for yourself most of the time. So if you just want to swim: go ahead.
Overall, exellent value for money and certainly my go-to address next time I come to Bangkok.